1. Field of the Invention
The present invention relates to a semiconductor device and more particularly, to a semiconductor device including a semiconductor element and a functional member (e.g., a semiconductor element, a transparent cover, and so on) fixed to the semiconductor element with an adhesive film.
2. Description of the Related Art
In recent years, the solid-state image pickup device has been being miniaturized and highly functionalized furthermore. In connection with this, more and more solid-state image pickup devices have been mounted on portable equipment, such as cellular phones and portable computers, and automobiles. In this way, the application field of the solid-state image pickup device is spreading still more.
In general, the solid-state image pickup device has a structure comprising a chip-shaped solid-state image pickup element, a chip-shaped cover (for example, a protection cover such as a glass cover) through which light transmits (in other words, transparent or translucent), and a Chip-Size Package (CSP) that encapsulates or encloses the image pickup element and the cover, wherein incident light passing through the cover is irradiated to the light-receiving areas of the image pickup element. The electrodes of the image pickup element are electrically connected to external electrodes provided on the package. The electric signals generated by the image pickup element in response to the incident light are lead to the outside of the image pickup device by way of the external electrodes.
The solid-state image pickup device is divided into two types. One of the types is the cavity type that comprises a minute gap (i.e., a cavity or an air gap) between the image pickup surface of the solid-state image pickup element and the cover. The other is the cavity-less type that does not comprise the cavity.
The solid-state image pickup device with the cavity has an advantage that the incident light is not affected by the refractive index of the cavity. However, this device has a disadvantage that the package including the cover (or the cavity) needs to be sealed hermetically, and that there is a possibility that the hermeticity degrades due to expansion and contraction of the gas existing in the cavity.
Unlike this, the solid-state image pickup device without the cavity (i.e., the cavity-less type solid-state image pickup device) needs not the above-described hermetic seal. However, this device requires attention to selection of a material placed between the image pickup surface and the cover (which may be termed an intermediate material). For example, it is necessary that the refractive index of the intermediate material is made as low as possible to bring it nearer to the refractive index (=1) of the air. In addition, to prevent the breakage of this device caused by the differences among the thermal expansion coefficients of the intermediate material, silicon and/or silicon dioxide that constitutes the image pickup element, and the transparent cover, it is necessary to consider the thermal expansion coefficient of the intermediate material, and the adhesion property or strength between the intermediate material and the cover. Moreover, if the hygroscopic property of the intermediate material is high, the image pickup element is likely to be affected badly by the moisture, which means that attention needs to be paid to the hygroscopic property.
By the way, the solid-state image pickup device with the hermetic-sealed cavity may comprise external electrodes on the back (i.e., the surface opposite to the cover) of the image pickup element. The electrical interconnection between these external electrodes and the electrodes formed on the surface of the chip-shaped image pickup element is often carried out using buried interconnection lines that penetrate through the silicon substrate of the image pickup element from its surface to its back. It is usual that the adhesion of the transparent cover (i.e., the protection member) to the surface of the image pickup element is performed using an adhesive made of synthetic resin.
A solid-stage image pickup device as a related-art technique relevant to the present invention is disclosed in the Patent Document 1 (the Japanese Non-Examined Patent Publication No. 2006-128648) published in 2006. This solid-state image pickup device comprises a wafer-level sensor body including sensor bodies arranged thereon with a dicing area; a corridor-shaped sealing frame placed in the an outside region of an active surface of each of the sensor bodies; and a wafer-size protecting material fixed to the wafer-level sensor body in such a way as to be opposed to the active surfaces of the respective sensor bodies by way of gaps. Each of the sensor bodies comprises terminals formed on an opposite surface of the active surface thereof and connected electrically thereto by way of penetrating vias. (See claim 1, FIGS. 1 to 2, and Paragraphs 0012 to 0016.)
When the wafer-level image pickup device of the Patent Document 1 is divided in the dicing area in such a way that the respective sensor bodies are separated from each other, chip-shaped image pickup devices are fabricated. With this chip-shaped image pickup device, as described above, the electrical connection between the electrodes formed on the surface of the chip-shaped image pickup device and the external electrodes formed on the back thereof is realized using the penetrating vias (i.e., buried interconnection lines) that penetrate through the chip-shaped image pickup device from its surface to its back. In addition, the adhesion of the sealing frame (i.e., cover) to the surface of the image pickup device is carried out using the sealing frame itself which is made of synthetic resin.
A sensor package as another related-art technique relevant to the present invention is disclosed in the Patent Document 2 (the Japanese Non-Examined Patent Publication No. 2007-165496) published in 2007. This sensor package comprises a sensor body having an active surface, a protecting material superposed on the sensor body to be in surface contact therewith in a periphery of the active surface in such a way that a gap is formed between the protecting material and the active surface; a connecting member fixed to the sensor body and the protecting material, on a side face of a stack of the sensor body and the protecting material, in such a way as to span over the sensor body and the protecting material, thereby hermetically sealing the gap; a minute penetrating hole formed to reach a part of the protecting material, which is opposed to the gap; and a blocking member located in the minute penetrating hole. (See claim 1, FIGS. 1 to 3, and Paragraphs 0009 to 0016.)
With the sensor package of the Patent Document 2, as described above, the electrical connection between the electrodes formed on the surface of the chip-shaped solid-state image pickup element and the external electrodes formed on the back thereof is performed by using the penetrating vias (i.e., buried interconnection lines) that penetrate through the image pickup element from its surface to its back. However, the fixing of the protecting material (i.e., cover) to the surface of the image pickup element is performed by using the connecting member fixed to the sensor body and the protecting material in such a way as to span over them on the side face of the stack. Therefore, the sensor package of the Patent Document 2 has a different structure from the above-described structure. This connecting member has a multilayer structure comprising a metal layer (e.g., a Au/Ti layer) formed on the side face of the stack, and a brazing material layer (e.g., a Sn—Au alloy layer), where any adhesive made of synthetic resin is not used.
With the hermetic-sealed solid-state image pickup device having the above-described structure, there is a problem that the moisture existing in the air enters gradually the inside of the cavity by way of the adhesive made of synthetic resin and as a result, the image-pickup performance degradation occurs because of the phenomenon that the cover and/or the image pickup surface is/are fogged or clouded due to the moisture thus entered.
To solve this problem, a metallic connecting member like the connecting member disclosed in the Patent Document 2 may be used. In this case, however, there arises a difficulty that not only the fabrication process steps are increased and complicated but also the fabrication cost is raised. Furthermore, because such the metallic connecting member is formed on the side face of the stack of the image pickup element and the protecting member (i.e., cover), this connecting member cannot be made by using the fabrication process steps that fabricate many solid-state image pickup devices in a lump where the covers are attached to the solid-state image pickup elements in a wafer level (i.e., on a wafer) and thereafter, the stack of the image pickup elements and the covers in a wafer level is divided into pieces by dicing, resulting in the solid-state image pickup devices. The said metallic connecting member needs to be formed after the image pickup elements on the wafer are separated by dicing. Thus, there is another difficulty that the fabrication process steps are highly disadvantageous.
The above-described difficulties or problems may occur not only in the solid-state image pickup devices but also any other types of the semiconductor device that comprises a semiconductor element and a functional member (e.g., another semiconductor element with a different function from the image pickup function, a transparent cover, and so on) fixed to the said semiconductor element with an adhesive film. This is because if moisture enters the inside of the cavity, the insulation property of the semiconductor device deteriorates, raising a problem of reliability decrease.
Moreover, even with the cavity-less semiconductor device, moisture may enter the inside of the semiconductor device by way of the adhesive film itself or the interface between the adhesive film and the member adjacent thereto. In this case, the reliability may degrade due to the moisture thus entered. Therefore, there is a possibility that the above-described problem relating to the reliability occurs in the cavity-less semiconductor device also.